When moving articles vertically between stations, including loading and unloading, it is desirable to provide a vertical shelf conveyor, wherein the articles are held on shelves that are moved vertically by means of one or more endless chains that are driven by engaging sprockets. To reduce space requirements, it is desirable to pivot the shelves from a horizontal load carrying position to a vertical return position used while the shelves travel along the return path of the endless chains. Stability of the shelves is highly desirable for conveying purposes.
A vertical conveyor such as that shown in the U.S. Pat. to Nesseth No. 2,869,708 issued Jan. 20, 1959, does not positively control the shelf position during the return run.
In tilting shelf conveyors such as shown in U.S. Pat. Nos. 2,747,724 issued May 29, 1956 and 3,365,052 issued Jan. 23, 1968, the shelves are under the control of two spaced apart tracks for each run, which requires considerable accuracy in the location and construction of the tracks, as well as expense in their manufacture and assembly. Further examples of such conveyors are U.S. Pat. Nos. 3,664,482 issued May 23, 1972; and 3,854,570 issued Dec. 17. 1974.